Usually, a glass or plastic container for a soft drink or the like has a mouth-and-neck portion on whose outer peripheral surface an external thread and an engaging jaw portion positioned below the external thread are formed. As is well known, a plastic container closure having tamper evident properties of the type disclosed, for example, in Japanese Patent Publication Nos. 32103/83 and 18421/87, Japanese Unexamined Patent Publication No. 311461/92, Japanese Unexamined Utility Model Publication No. 54544/94 and Japanese Unexamined Patent Publication No. 80957/96 has found widespread use for such a container. The container closure has a circular top panel wall, and a skirt wall extending downwardly from the top panel wall. The skirt wall has formed therein a circumferentially extending circumferential breakage means, which divides the skirt wall into a main portion above the circumferential breakage means, and a tamper evident bottom portion below the circumferential breakage means. The main portion of the skirt wall has formed on its inner peripheral surface an internal thread collaborating with the external thread formed in the mouth-and-neck portion of the container. The tamper evident bottom portion has formed on its inner peripheral surface an engaging means collaborating with the engaging jaw portion formed in the mouth-and-neck portion of the container. The circumferential breakage means includes a plurality of bridging portions disposed at circumferentially spaced positions and connecting the tamper evident bottom portion to the main portion of the skirt wall. One of the plurality of bridging portions is a high strength bridging portion having a large cross-sectional area. In the tamper evident bottom portion, axial breakage means is formed. The axial breakage means is constituted from a score formed by reducing the thickness of the material, or a slit including a discontinuous portion (a groove formed by either completely cutting the material in its thickness direction, or causing the material not to be present in the entire thickness direction during molding).
To seal the mouth-and-neck portion of the container by mounting the container closure thereon, the container closure is fitted on the mouth-and-neck portion, and turned in a closing direction to screw the internal thread of the container closure onto the external thread of the mouth-and-neck portion. As the screwing together of the external thread and the internal thread proceeds, the container closure is brought downward. The engaging means of the container closure is elastically passed over the engaging jaw portion of the mouth-and-neck portion and engaged with the surface below the engaging jaw portion. To unseal the mouth-and-neck portion of the container, the container is turned in an opening direction. As a result, the internal thread of the container closure is moved along the external thread of the mouth-and-neck portion, whereupon the screwing together of the external thread and the internal thread is released. Thus, the container closure is brought upward in accordance with turning in the opening direction. However, the engaging means formed in the tamper evident bottom portion remains engaged with the engaging jaw portion of the mouth-and-neck portion. Hence, the tamper evident bottom portion is inhibited from ascending. Because of this inhibition, stress is generated in the circumferential breakage means, whereby the bridging portions in the circumferential breakage means are broken, except for the one high strength bridging portion. Furthermore, occurrence of the following behavior has been contemplated: The score or the discontinuous portion of the slit in the axial breakage means formed in the tamper evident bottom portion will be broken. Thus, the tamper evident bottom portion will be spread in the form of a band, whereby the engaging means will be disengaged from the engaging jaw portion. Then, the entire container closure will be moved upward in accordance with the turning in the opening direction, and removed from the mouth-and-neck portion.
According to the experience that we, the inventors, have, the conventional container closure described above poses the following problem: In unsealing the mouth-and-neck portion of the container, it has been intended that the score or the discontinuous portion of the slit in the axial breakage means formed in the tamper evident bottom portion will be broken, so that the tamper evident bottom portion will be spread in the form of a band. However, the one high strength bridging portion in the circumferential breakage means may be broken instead of the breakage of the score or the discontinuous portion of the slit in the axial breakage means. As a result, the score or the discontinuous portion of the slit may remain unbroken. This may result in the event that the tamper evident bottom portion in an endless annular shape is completely separated from the main portion of the skirt wall, and this endless annular shaped tamper evident bottom portion remains on the mouth-and-neck portion of the container, while the other portions of the container closure are removed from the mouth-and-neck portion. If this event happens, the task of cutting off the endless annular shaped tamper evident bottom portion by a suitable cutting tool to remove it from the mouth-and-neck portion of the container in a band-like spread form will have to be performed separately, from the point of view of material-wise collection of wastes or for the purpose of container recycling.
To solve the foregoing problem with the conventional container closure, it is intended to constitute the axial breakage means, disposed in the tamper evident bottom portion, from a slit continuously extending from the upper end of the tamper evident bottom portion substantially to its lower end. By so doing, when the mouth-and-neck portion of the container is to be unsealed, the bridging portions in the circumferential breakage means are broken, except for the one high strength bridging portion, whereupon the tamper evident bottom portion is necessarily spread in a band form. Thus, the entire container closure is removed from the mouth-and-neck portion of the container fully reliably. However, constituting the axial breakage means, disposed in the tamper evident bottom portion, from a slit continuously extending from the upper end of the tamper evident bottom portion substantially to its lower end tends to cause the following unacceptable event: When the container closure is mounted on the mouth-and-neck portion of the container, especially when the engaging means of the container closure elastically passes over the engaging jaw portion of the mouth-and-neck portion, the tamper evident bottom portion is enlarged at the site where its axial breakage means exists. This causes breakage of at least some of the plurality of bridging portions in the circumferential breakage means.